Make the `GoldDescriptor` serializable

**Context & Problem** One core principle of Goldener is the on demand access to pipelines! To enable this for the description of data, it is required to have a way to load/create back a previously created `GoldDescriptor`. So far, the only way to store a `GoldDescriptor` is to pickle it. This is unfortunately not so convenient when the design of objects can still evolve. Let's define the serialization format for the `GoldDescriptor`! **Proposed Solution** Following the design principle decided in https://github.com/goldener-data/goldener/issues/284: - make `GoldEmbeddingTool` serializable - make `TensorVectorizer` serializable - make `GoldDescriptor` serializable